1. Field of the Invention
The present invention is directed to a control device of an internal combustion engine and a method of controlling the same. In particular, the present invention is directed to a control device of an internal combustion engine and a method of controlling the same which make it possible to restrict an unexpected change in the purification ability of the catalyst while suppressing the fuel economy deterioration and emission deterioration which are associated with an intervention in the air-fuel ratio control, the internal combustion engine being provided with an exhaust gas purification device wherein a catalyst is used whose active element forms a solid solution component in a carrier if a temperature of the catalyst is equal to or more than a predetermined first solid solution temperature and an internal atmosphere of the catalyst is an oxidizing atmosphere and whose active element is precipitated from the carrier if the temperature of the catalyst is equal to or more than a predetermined deposition temperature and the internal atmosphere of the catalyst is a reducing atmosphere.
2. Description of Related Art
In the technical field concerned, an exhaust gas purification device is known that has an exhaust gas purification catalyst for purifying a specific component contained in an exhaust gas emitted from an combustion chamber of an internal combustion engine. In general, such an exhaust gas purification catalyst includes an element serving for activating an oxidizing reaction or a reducing reaction of a specific component contained in the exhaust gas (hereinafter, such an element is sometimes referred to as “active element”) and a carrier serving for carrying the active element. Regarding such a catalyst, as well known, during use, the catalyst's ability of purifying the specific component in the exhaust gas (which is sometimes referred to as “purification ability” in this specification) is deteriorated which results from the reduction of the outer surface in accordance with the grain growth due to the aggregation of the active element (for example, noble metal element having catalytic activity).
Thus, in the technical field concerned, as the catalyst having the above described structure, a substance is widely used, which has a carrier formed of a composite oxide, has characteristics wherein the active element forms a solid solution component in the carrier if an internal atmosphere of the catalyst is an oxidizing atmosphere, while the active element is deposited from the carrier if the internal atmosphere of the catalyst is a reducing atmosphere. Such a catalyst, depending on the internal combustion engine operation condition, repeats the solid solution of the active element in the carrier (composite oxide) in the oxidizing atmosphere and the deposit of the active element from the carrier in the reducing atmosphere, thereby restricting the aforementioned grain growth (see, for example, International Publication No. 2008/096575 (WO 2008096575)).
However, during operation of the internal combustion engine, depending on the internal combustion engine operation condition, the temperature of the catalyst (sometimes referred to as “catalyst temperature” in this specification) and an air-fuel ratio of the exhaust gas entering the catalyst (sometimes referred to as “exhaust gas-fuel ratio” in this specification) vary. More specifically, the catalyst temperature sometimes reaches a temperature at which the active element can form a solid solution component in the carrier (which is sometimes referred to as “specific solid solution temperature” in this specification) or reach a temperature at which the active element can deposit from the carrier (which is sometimes referred to as “specific deposition temperature” in this specification). In addition, the exhaust gas-fuel ratio become leaner or richer than a theoretical air-fuel ratio. As a result, the internal atmosphere of the catalyst is sometimes the oxidizing atmosphere and otherwise the reducing atmosphere.
Thus, when the catalyst temperature is equal to or more than the specific solid solution temperature and the internal atmosphere of the catalyst is the oxidizing atmosphere, forming of the solid solution of the active element in the carrier proceeds, while when the catalyst temperature is equal to or more than the specific deposit temperature and when the internal atmosphere of the catalyst is the reducing atmosphere, the deposition of the active element from the carrier proceeds. Sometimes the internal combustion engine operation condition may unbalance the solid solution and deposition of the catalyst as described above, which reduces an amount of the active element which is capable of developing a catalytic function (i.e., the active element which is deposited from the carrier), resulting in that the purification ability of the catalyst may change. In addition, as described above, as is known, during use, the catalyst's ability of purifying the specific component in the exhaust gas (which is sometimes reoffered to as “purification ability”) is deteriorated which results from the shrinkage of the outer surface in accordance with the grain growth due to the aggregation of the active element.
In view of the above, with respect to the exhaust gas purification catalyst that is related to the present invention, attempts have been made in which by, for example, inhibiting a fuel cut control (hereinafter, such a control is referred to as “FC control”) in a case where the catalyst temperature is equal to or more than the specific temperature, the solid solution of the active element in the oxidizing atmosphere is prevented from being proceeded in order to restrict the degradation of the catalyst purification ability caused by the grain growth of the active element and an amount fuel is increased to lower the temperature of the catalyst for the prevention of possible thermal deterioration thereof. In brief, the design concept of the aforementioned exhaust gas purification catalyst focuses on the restriction of the deterioration of the catalyst which is to be achieved by setting the initial purification ability of the catalyst at a high level based on forecasting the deterioration of the catalyst.
The aforementioned related art will be detailed with reference to the attached drawings. FIG. 1 is a graph that schematically indicates the purification ability transition diagram throughout the useful life (effective life or service life) of an exhaust gas purification catalyst according to a related art of the present invention. In the graph shown in FIG. 1, an abscissa represents a use period of a catalyst (for example, if an internal combustion engine is mounted on an automotive vehicle, the mileage of the vehicle is available as this period), while an ordinate represents a content percentage of a specific component in an exhaust gas (hereinafter, sometimes referred to as “emission”). Thus, in FIG. 1, the curve depicted by a thin solid line represents a transition of the purification ability throughout the use period of the exhaust gas purification catalyst according to the related art.
In the exhaust gas purification catalyst according to the related art that is illustrated in FIG. 1, as described above, the design of this catalyst sets the initial purification ability to be at a high level by forecasting the possible catalyst degradation in order that even when the emission is degrades (even the content percentage of the specific component in the exhaust gas increase) caused by the catalyst deterioration during use, the emission is restricted to exceed a predetermined upper limit (plotted by a thin dotted line in FIG. 1). Thus, in cases where, for example, the purification ability of the exhaust gas purification catalyst is requested to increase by, for example, enhancement of emission regulations (indicated by a black arrow in FIG. 1) and where the useful life is requested to get longer (indicated by a void arrow in FIG. 1), the purification ability of the catalyst has to be designed so as to be able to achieve a lower emission level even in a final stage as the curve line plotted by the thick solid line shown in FIG. 1.
In addition, for confirming whether the catalyst that is designed by the aforementioned concept can maintain the desired purification ability throughout the useful life (effective life or service life), it was inevitable to repeat processes each of which requires significant man-hour and which includes performing different durability tests (including acceleration tests), assessing the content percentage of the specific component in the exhaust gas (emission) emitted from the combustion chamber of the internal combustion engine in which is used the catalyst after the durability tests and other items, and reviewing the design specifications of the catalyst.
Furthermore, while the aforementioned internal combustion engine is in operation, in order to allow the internal combustion engine to exhibit its performances in the event of a change of the purification ability of the catalyst, it is required to construct a control logic for use in a control related to the internal combustion engine which takes into account of such a change of the purification ability of the catalyst (hereinafter, such a control sometimes may be referred to as “engine control”), and executing such an engine control on the basis of thus constructed control logic. However, as described above, due to the fact that the change of the purification ability of the catalyst while the internal combustion engine is in operation is affected by, for example, the internal combustion engine operation conditions and the use degree of the catalyst, it is extremely cumbersome to construct the control logic that takes into account of the aforementioned change of the purification ability of the catalyst and to execute the engine control.
In view of the above, in the technical field concerned, various attempts have been proposed, wherein the aforementioned change of the purification ability of the catalyst is controlled by a positive intervention in the air-fuel ratio control being performed while the internal combustion engine is in operation, for example. For example, a technique has been proposed for preventing the catalyst activity deterioration in which a time during which the catalyst is being exposed to the exhaust gas of lean air-fuel ratio at equal to or a higher temperature than a predetermined temperature is integrated as a high lean time, and the engine air-fuel ratio is switched to rich when the high temperature lean time comes to be a predetermined time or more, thereby depositing a catalyst metal, which forms a solid solution component in a support material formed of an oxide, therefrom (see, for example, Japanese Patent Application Publication No. 2006-183624 (JP 2006-183624 A)).
In addition, the present applicant has proposed a technique in which the exhaust gas-fuel ratio is made to be leaner than a theoretical air-fuel ratio in a case where the solid solution of the active element is equal to or less than the target value or the lower limit value of the target range and the catalyst solid solution temperature is equal to or more than the specific solid solution temperature, while the exhaust gas-fuel ratio is made to be richer than the theoretical air-fuel ratio in a case where the solid solution of the active element is equal to or more than the target value or the upper limit value of the target range and the catalyst temperature is equal to or more than the specific deposit temperature. Moreover, the present applicant has also proposed a technique in which in a case where the fuel supply stop control is inhibited when the catalyst temperature is equal to or more than a first threshold vale, so long as the use degree of the catalyst is being equal to or less than a predetermined degree, the first threshold value is reduced from its criteria to a lower value, while in a case where the fuel supply stop control is permitted when the catalyst temperature is equal to or more than a second threshold value, so long as the use degree of the catalyst is being equal to or less than the predetermined degree, the second threshold value is increased from its criteria to a higher value.
In any of the techniques as described above, the positive intervention in the air-fuel ratio control that is being performed while the internal combustion engine is in operation makes it possible to control the aforementioned change of the purification ability of the catalyst, whereby for example a relatively easy construction of a control logic for use in the engine control and a relatively easy performance of the engine control can be established.
However, recently, many internal combustion engines, from the viewpoints of, for example, energy efficiency and protecting global environment, perform an advanced air-fuel ratio control in order to establish both high operational performance and improvement in fuel and emission. Thus, making the aforementioned positive intervention in the air-fuel ratio control to control the change of the purification ability of the catalyst may sometimes reduce the improved effects of the fuel efficiency and emission which are achieved by the air-fuel ratio control, which may results in a fear of deteriorating the fuel efficiency and emission.
Thus, in the technical field concerned, regarding an internal combustion engine provided with an exhaust gas purification device that uses a catalyst whose active element forms a solid solution component in a carrier if a temperature of the catalyst is equal to or more than a predetermined first solid solution temperature and if an internal atmosphere of the catalyst is an oxidizing atmosphere and whose active element is deposited from the carrier if the temperature of the catalyst is equal to or more than a predetermined deposition temperature and if the internal atmosphere of the catalyst is a reducing atmosphere, there is a need for solution that is capable of restricting an unexpected change in the purification ability of the catalyst while suppressing the fuel economy deterioration and emission deterioration which follow an intervention to the air-fuel ratio control.